Control apparatus



June 1, 1965 P. J. WALSH 3,187,221

CONTROL APPARATUS Filed April 10, 1963 INVENTOR United States Patent3,187,221 CONTROL APPARATUS Philip J. Walsh, 239 Phelan Ave., SanFrancisco, Calif. Filed Apr. 10, 1963, Ser. No. 272,164 2 Claims. (Cl.315-182) This invention relates to apparatus for operating gas dischargetubes, as for example, fluorescent lamps and sign tubing.

Fluorescent tubes are characterized by the fact that the greater thecurrent through them, the lower the voltage they require. If supplied bya constant voltage source, the current through them will increase to avalue that destroys the tube. To prevent this in conventional types, aballast impedance is included in circuit with the tube, which drops thevoltage across it as the current increases, the impedance usually beingbuilt into the transformer as leakage reactance. Accordingly thetransformer must be built to supply a much higher voltage on opencircuit than is required across the tube in normal operation.Furthermore, a different voltage transformer is required for eachdifferent length of tube. Tubes cannot be operated in parallel, for ifthey were, one would carry all of the current and be destroyed.Conventional transformers are bulky in comparison to their power outputand correspondingly expensive. They operate at a low power factor i.e.,the power company must supply a large current in relation to the powersupplied, and therefore the rate charged for the power used isrelatively high.

Among the objects of the present invention are to provide automaticcontrol apparatus for the operation of gas discharge tubes of the samelength and diameter, or of dilierent lengths and diameters in paralleland supplied by a common source such as a transformer. Further it is anobject to provide means to control the switching action of the parallelgas discharge tubes and their series condensers so as to produce stableoperation and good waveform of the current flowing through the tubes formaximum light output.

Referring to the drawing:

The single figure is a system diagram depicting one form of myinvention.

In the drawing, I show a source of alternating current power 1 connectedthrough the switch 3 to the primary winding 5 of the transformer 7having the secondary winding 9. This transformer is preferably of thelow reactance type described and claimed in my patent, Number 2,875,378.The two gas discharge tubes 11 and 13 can be of any length up to thelimit determined by the value of the voltage supplied by the secondary9. Many tests of the invention were made using two tubes of the samelength and diameter, two tubes of diflferent lengths, and two tubes ofdifferent diameters. Satisfactory operation of the tubes occurred in allof the tests. The waveform of the tube current, and switching action ofthe tubes can be changed by adjustment of the rheostat 15 to producemaximum light output from the tubes.

When the arm 17 of the rheostat 15 is moved to the point 21, theresistor is short circuited, the condensers 23 and 25 are connected inparallel and all of the current flows through only one of the tubes.That is, only the tube that is electrically shorter than the other tubewill light up.

When the arm 17 is moved to the point 19, the resistor is disconnectedand the switching action of the tubes is such as to produce many currentpulses through each tube for each half cycle of the fundamentalfrequency of the source 1. The tubes switch on and off, one at a time,one is on while the other is off. The action can best be described bystarting With a charge of the same polarity in each condenser. That is,when switch 3 is opened, it will Patented June 1, 1965 be found that ifthe right hand terminal of condenser 23 is plus, the right hand terminalof condenser 25 will also be plus as shown by the plus and minus signsin the drawmg.

Now let us assume that both condensers are charged so that both righthand terminals are plus and that the half cycle of the voltage acrosscoil 9 is'building up from zero value and making its left hand terminalplus, and that the tube 11 is electrically shorter than the tube 13.When the voltage across coil 9 in series with the voltage acrosscondenser, 23 is high enough to strike an arc in tube 11, tube 11switches on and condenser 23 discharges through tube 11. This causes areduction in the value of the voltage across secondary 9 and the voltageacross condenser 23 falls to a low value. Thus the voltage across tube11 falls to a value too small to maintain the are through tube 11, sothe tube switches olf. The half cycle of voltage across coil 9 continuesto rise and when the voltage value across tube 13 reaches its strikingvalue, tube 13 switches on and condenser 25 discharges through tube 13.At this point both condensers are discharged and no current flowsthrough the tubes. But the value of the voltage across coil 9 is stillrising and when it reaches the striking value of the tube 11, tube 11switches on and condenser 23 is charged in the opposite direction, asillustrated by the plus and minus signs in circles. The voltage built upacross condenser 23 bucks the voltage across coil 9 and tube 11 switchesoff leaving a charge in condenser 23 of the polarity illustrated by theplus and minus signs in the circles. When the value of the voltageacross coil 9 reaches the striking value of tube 13, tube 13 switches onand condenser 25 takes a charge and of the polarity shown by the plusand minus signs in the circles. At this point, with both condenserscharged and both tubes switched ofr', the voltage across coil 9 suddenlydrops from its peak value to zero. When the next half cycle of voltagebuilds up across coil 9, making its terminals plus and minus asillustrated by the plus and minus signs in the circles, the actions justdescribed repeat.

With the arm 17 set on point 19 the system requires careful adjustmentof the voltage of the source 1 and tube lengths to avoid flicker and toobtain stable operation.

By means of the rheostat 15, stable operation is ob- 'tained, the timingof the switching action controlled and tube current waveforms for bestlight output obtained. The setting of the rheostat 15 is not critical.The rheostat 15 can be adjusted to a value of resistance that causesboth tubes to switch on and off together and the current through thetubes can be made to approach sine wave form.

In one of the tests of this invention, tube 13 was made up of severallengths of 15 millimeter mercury sign tubing connected in series, tomake a total length of 45 feet. Tube 11 was made up of the same kind oftubing connected in series, to make a total length of 40 feet. Each ofthe condensers had a value of .025 microfarad. The

value of the current through each tube, as measured by a thermalmilliammeter, was 50 milliamperes. The noload voltage across coil 9 was4300 volts R.M.S. The input power was 325 watts and the power factor was91%. Rheostat 15 had a value of about 60,000 ohms. The loss in resistor15 was about 6 watts. The total length of tubing lighted up by thissmall low voltage light weight control unit was feet. The potted casedunit weighed about 20 pounds.

According to the tube footage chart, published by the manufacturers ofconventional luminous tube transformers, to light 85 feet of 15millimeter mercury tubing, would require two 9,000 volt, 60 milliamperetransformers. 42.5 feet of tubing connected across each trans- 7 Thetest circuit described is only one of the many pos-- sible ones'and itis not intended as limiting the scope of the invention as defined in'the claims that -follow.

I claim: 7 1. In a gas-discharge tube lighting circuit, a pair of gasdischarge tubes adapted for connection to a source of alternatingcurrent power, a single reactor comprising a condenser connected inseries with each tube, and variable impedance means connected from onecondenser to the other condenser, whereby the timing of the switchingaction of said tubes and the waveform of the current in said tubes canbe changed by adjustment of said variable impedance.

2. The combination as defined in claim 1 wherein said variableimpedance, means comprises a variable resistor.

No references cited.

10 DAVID J. GALVIN, Primary Examiner.

1. IN A GAS-DISCHARGE TUBE LIGHTING CIRCUIT, A PAIR OF GAS DISCHARGETUBES ADAPTED FOR CONNECTION TO A SOURCE OF ALTERNATING CURRENT POWER, ASINGLE REACTOR COMPRISING A CONDENSER CONNECTED IN SERIES WITH EACHTUBE, AND VARIABLE IMPEDANCE MEANS CONNECTED FROM ONE CONDENSER TO THEOTHER CONDENSER, WHEREBY THE TIMING OF THE SWITCHING ACTION OF SAIDTUBES AND THE WAVEFORM OF THE CURRENT IN SAID TUBES CAN BE CHANGED BYADJUSTMENT OF SAID VARIABLE IMPEDANCE.